PORTSMOUTH — One day after work began at the future site of the African burial ground memorial park, city crews and archaeologists found the remains of five bodies while digging at the site Thursday.

The discovery threatens the viability of design plans for the Chestnut Street park, which are more than four years in the making.

A series of 13 coffins were discovered during an infrastructure project on the street in 2003. Experts later determined the remains were part of the "Negro Burying Ground" shown on a 1705 city map.

The boundaries of the burial ground are unknown, but archaeologists said they believe there could be up to 200 bodies underneath Chestnut Street, between Court and State streets.

On Wednesday, the city began excavating along the surface in a small section of the street to ensure there would be no further disturbance when foundation and drainage work was done for the parks. On Thursday morning, crews had found skull fragments that appeared to have been crushed by a metal gas pipe laid there. Other bone fragments were found throughout the day, as well as wooden coffins.

Kathy Wheeler, of Independent Archaeological Consulting, was at the scene in 2003 and was there when the remains were found Thursday. The discovery was not a huge surprise, she said, but they had hoped the burials would be deeper to allow for the park to be constructed.

"The purpose was to confirm the absence of graves in the 2½ feet they need to put the memorial there. And we've in fact proved that they can't go everywhere 2½ feet because there are some burials that shallow," said Wheeler. "It renews all sorts of discussions we've already had."

The project will likely have to be modified, according to Deputy City Manager Cindy Hayden, but it unknown to what extent. The city canceled a meeting scheduled for Monday to unveil the final design to the public, in order to determine how to proceed.

"The balancing act we face is we want to create a memorial there that honors the burial ground, but at the same time, we don't want to further disturb those buried there," Hayden said.

Most of the bones discovered were fragments, but Wheeler said inside one of the coffins appeared to be a complete skull. She said it will be up to the African-American community to decide whether to disinter the remains and attempt to learn more about the people buried there or leave them buried.

Valerie Cunningham, a local black historian and member of the African Burying Ground Committee, said she is disappointed the design the committee worked so hard on will have to be modified.

"It re-emphasizes what we've been trying to say all along — that we don't know the barriers of the burial ground," said Cunningham. "We never thought that was it, and we still don't know how far it goes."

While it is unfortunate the design plans must change, Hayden said, she is happy the city decided to do the test dig.

"We didn't want to spend more money on the final engineering design, put it out to bid and hire a contractor and, on Day 1, find what we did today," said Hayden. "So we'll look at the design, consult with the state archeologist and find out how we can make something work there."